In the time division duplex (TDD) radio communication network such as TDD long term evolution (LTE), there is an inevitable propagation delay between the access point (AP) and the user equipment (UE). When performing UL transmission to the AP, the UE is required to set a timing advance offset. Traditionally, for the very first UL transmission, i.e., the transmission of the physical random access channel (PRACH), the UE is set a fixed timing advance offset NTA offset in hardware to handle the downlink-to-uplink switching time as illustrated in FIG. 1, which however doesn't cover the variance of DL and UL timing difference at AP side, which is assumed to be fixed as zero or small enough to be ignored.
However, with the introduction of the self-backhaul in the TDD radio communication system, one or more relay APs exist between the donor AP and the UE to relay the random access request from the UE to the donor AP, which is motived by the more limited coverage of a single hop when higher frequency band is applied to the backhaul link, e.g., using millimeter wavelength frequency. In this case, the accumulated propagation delay between the donor AP and the UE is hard to be ignored. If the accumulated propagation delay is not taken into account when the UE sends a random access request to the relay AP through the PRACH, the random access request will arrive at the relay AP later than expected and thus probably miss the time slot assigned for the relay AP to receive the random access request. Hence, the PRACH transmission timing error may cause failure in the random access procedure. In addition, due to the delay, the random access request may arrive at the relay AP overlapping with the time slot afterwards which is scheduled to perform reception for other channels such as physical uplink shared channel (PUSCH) transmission. As such, the undesirable interference occurs.